My GM has mentioned something called "lord and saviour mwk studded leather armour barding" which he says has no armor check penalty. But I can't find this anywhere. Does anybody have a link or know the source?
All normal studded leather, whether armor or barding, has an ACP of -1. So all mwk studded leather (in either form) has ACP 0.
"Lord and savior" would just be your GM's colorful way of appreciating how useful the stuff is for protecting your animal companion w/o messing it up or spending its feats on armor proficiency. It is not a game term.
The above post is accurate. 0 ACP for wearing armor without profiency is also often seen with Mithral Chain Shirt, Mithral Kikko, Mithral Breastplate of Comfort and, for humanoids, mithral buckler (in increasing expense), but Masterwork Studded Leather is the cheapest by far if you don't need to worry about arcane spell failure.